20D master/slave flash quesion. HELP..

[johneric8]

I set my sunpak external falsh on a tripod today and put it about 15 degrees left of my subject. I was using the on camera flash to trigger the external sunpak flash that was on the tripod. Okay, now, here is my question and it might be a stupid one for all yee experts out there. Is there a way I can trigger the external flash without the internal built in flash going off? Does the slave know to flash because of the master flash or is it some infarred signal? I got the slave to go off, but I think my results were poor because of the two flashes.. Any info you have on making this type scenario work would be awesome!! It was about 6pm and the sun was going down so I exposed for the ambient light then tried to illuminat my subject with the external flash. I think it would have been cool if I didnt have to use the flash on the camera to make the other flash go off. Forgive me if this is a stupid question... I know there is a custom menu feature about the flash on the 20D I'm just now sure if it has a setting that will allow this...

[Tom Reid]

Where was the sunpack plugged in....via the hot shoe on the 20D and a cord??

[johneric8]

Where was the sunpack plugged in....via the hot shoe on the 20D and a cord??

the sunpak wasnt plugged in. It was set to slave and the on camera built in flash was triggering it. Basically, the sunpak was on a tripod not attached to a camera set to slave. The 20D was firing it's flash as normal and setting off the sunpak. My question is, is it the flash itself on the 20D that sets of the sunpak (slave) or, is it an infarred signal or something like that? I just wanted to be able to trigger the sunpak flash without the 20d's flash going off.. If it's not possible that is cool I was just curios.. If anyone has any experience doing this and making it work please give me some details on flash setting on the external flash?

[robertwgross]

You might want to stop and sort out what you are trying to do.

1. Trigger the external flash from a PC sync cord.
---or---
2. Trigger the external flash as a wireless slave doing the Canon wireless flash system.
---or---
3. Trigger the external flash optically.

Canon will support 1 or 2, but I have some doubts about that flash doing 2, and you don't have a wireless master to do 2.

If that flash will do 3, then what's it going to trigger from, the first pre-flash pop, or the main flash pop an instant later? Hint: if it from the pre-flash, then it fails. If it goes from the main pop, then it has a chance.

---Bob Gross---

[kawter2]

= My question is, is it the flash itself on the 20D that sets of the sunpak (slave) or, is it an infarred signal or something like that?


it is the 20D's flash light is what triggers your sunpack..

[SkipD]

it is the 20D's flash light is what triggers your sunpack..It is highly probably that the 20D's flash is emitting a pre-flash for the purpose of determining the exposure setting. This pre-flash is probably triggering your remote slave flash.

The net result is likely to be: 1) The slave flash triggers before the shutter opens and thus does not contribute to your photo. 2) The slave flash might be adding to the light detected by the camera during the pre-flash phase and upsetting the exposure calculation for the main flash.

Possible solution: If the camera's flash can be made to NOT emit a pre-flash, then you might make things work. I checked my 20D, and it seems that in M (manual) mode, the pre-flash does not go off. If this is true (it was difficult to tell for sure), then you should be able to set the camera into manual mode, use the on-camera flash as a master to fire your slave flash, and adjust the aperture setting manually to achieve the exposure you need. The shutter speed would have to be set to something equal to or slower than 1/250th.

A good test to see if the slave flash is triggering at the right time is to point it at the camera and take a photo. If you can see the slave flash illuminated in your photo, then it is triggering at the time the shutter is open.

[PacAce]

Is there a way I can trigger the external flash without the internal built in flash going off?
Yes, there is. As a matter of fact, there are several options.

1) Attach a 550EX or 580EX flash and set it to manual mode. In manual, these flashes will not fire a pre-flash so your slave will not be triggered prematurely.
2) Attach a compatible thyristor-controlled flash. Again, there will be no pre-flash to prematurely trigger the slave.
3) Use a PocketWizard to trigger and remotely fire the slave.

However, if what you meant was is there's a way to trigger the slave without any other flash going off or using an RF remote or wire, then the answer is a big NO.

[johneric8]

thanks guys. I know it's kind of a stupid question but I thought I would see what ya thought.. It makes sense that there has to be a flash on camera to set off the slave. I just didnt have my setting right at the shoot. I didnt get very flattering light. Live and learn..

[mbze430]

Yep, sounds like your internal built-in flash 20D is pre-triggering your Sunpak, so really you are just getting the normal frontal direct light.

As others have suggested. If the sunpack has a PC Sync outlet, you can use the PC Sync on the 20D, and a PC cord to trigger it.

You can also buy a PC Sync terminal hot shoe for your sunpack, and use the same method described above.

You can use a 550 or 580, you can turn off the flash head on the unit so that it will not pop during the open curtain.

Lastly you can use a ST-E2 with a piece of masking tap on the 4 prongs. This will disable the ST-E2 from going to ETTL mode, and only trigger the IR light in manual mode.

Lastly you can get wireless transmitter and receiver to set off the flash head, via PocketWizard.